1. Field of the Invention
The present invention relates, in general, to an apparatus used within a varying magnetic field and, in particular, to an apparatus used between magnetic poles of a magnet of a synchrotron.
2. Description of the Related Art
A synchrotron used in various fields including scientific researches, and medical and industrial applications, orbits and, at the same time, rapidly accelerates a charged particle beam injected from a pre-accelerator. The synchrotron typically includes an injection apparatus that injects the charged particle beam that have been preliminarily accelerated by the pre-accelerator, a dipole magnet that bends and moves the charged particle beam around a predetermined circular path, a quadrupole magnet that gives horizontal and vertical converging forces so as to prevent an orbiting beam from being widened, and an RF cavity that applies an RF acceleration voltage to the orbiting beam to thereby accelerate the orbiting beam to a predetermined level of energy.
In order to circulate the charged particle beam along a predetermined orbit at all times, the synchrotron intensifies the magnetic field generated by the dipole magnet in synchronism with the acceleration. Since the charged particle beam circulates in vacuum, the synchrotron includes a vacuum duct with an evacuated interior disposed between magnetic poles of the dipole magnet. If the vacuum duct is formed of a conductive substance, an induced electric field causes an eddy current to flow through the vacuum duct. The eddy current induced in the vacuum duct generates a new magnetic field in an area past which the charged particle beam moves. This magnetic field has varying intensities depending on the position at which the charged particle beam moves, which unsteadies circulation of the charged particle beam.
JP-08-78200-A discloses art in which a nonmagnetic correcting plate is disposed between magnetic poles of the dipole magnet to thereby flatten a magnetic field which an eddy current generates in an area past which the charged particle beam moves. JP-03-190099-A discloses art that prevents a distribution of a magnetic field generated in a vacuum duct from being disturbed by continuously increasing a thickness of a vacuum duct of a synchrotron from a central portion toward end faces.